Conventional lithographic printing techniques cannot accommodate true high-speed variable data printing processes in which images to be printed change from impression to impression, for example, as enabled by digital printing systems. The lithography process is often relied upon, however, because it provides very high quality printing due to the quality and color gamut of the inks used. Lithographic inks are also less expensive than other inks, toners, and many other types of printing or marking materials.
Ink-based digital printing as discussed in this disclosure uses a variable data digital lithography printing system, or digital offset printing system. A “variable data digital lithography system” is an image forming system that is configured for lithographic printing using lithographic inks and based on digital image data, which may be variable from one image to the next. “Variable data lithography printing,” or “digital ink-based printing,” or “digital offset printing” are terms that may be generally interchangeably employed to refer to the processes of lithographic printing of variable image data for producing images on a wide latitude of image receiving media substrates, the images being changeable with each subsequent rendering of an image on a substrate in an image forming process.
For example, a digital offset printing process may include transferring radiation-curable ink onto a portion of a fluorosilicone-containing imaging member surface that has been selectively coated with a dampening fluid layer according to variable image data. The ink is then cured and transferred from the reimageable surface of the imaging member to an image receiving media substrate such as paper, plastic, or metal on which the image is printed. The reimageable surface of the imaging member may be then cleaned and used to form a succeeding image that is different than the preceding image, based on the variable image data. Ink-based digital printing systems are variable data lithography systems configured for digital lithographic printing that may include an imaging member having a reimageable surface layer, such as a silicone-containing surface layer.
Systems may include a dampening fluid metering system for applying dampening fluid to the reimageable surface layer, and an imaging system for laser-patterning the layer of dampening fluid according to image data. The dampening fluid layer is patterned by the imaging system to form a dampening fluid pattern on a surface of the imaging member based on variable data. The imaging member is then inked to form an inked image based on the dampening fluid pattern. The inked image may be partially cured as appropriate to adjust a rheology of the ink forming the inked image. The inked image may them be transferred to a printable image receiving media substrate. An objective is to achieve a transfer efficiency exceeding 95%. The reimageable surface of the imaging member from which the inked image is transferred is cleaned to remove residual ink and dampening fluid from the reimageable surface in preparation for forming a further image that may be different from a previous image, or based on different image data than the image data used to form the previous image. Such systems are disclosed in U.S. patent application Ser. No. 13/095,714 (“714 Application”), entitled “Variable Data Lithography System,” filed on Apr. 27, 2011, by Timothy Stowe et al., which is commonly assigned, and the disclosure of which is hereby incorporated by reference herein in its entirety.